radix-tree: rewrite radix_tree_tag_get

Use the new multi-order support functions to rewrite
radix_tree_tag_get()

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/radix-tree.c

@@ -831,45 +831,37 @@ EXPORT_SYMBOL(radix_tree_tag_clear);
 int radix_tree_tag_get(struct radix_tree_root *root,
 			unsigned long index, unsigned int tag)
 {
-	unsigned int height, shift;
-	struct radix_tree_node *node;
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+	unsigned int shift;
 
-	/* check the root's tag bit */
 	if (!root_tag_get(root, tag))
 		return 0;
 
-	node = rcu_dereference_raw(root->rnode);
+	shift = radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return 0;
 	if (node == NULL)
 		return 0;
 
-	if (!radix_tree_is_indirect_ptr(node))
-		return (index == 0);
-	node = indirect_to_ptr(node);
-
-	height = node->path & RADIX_TREE_HEIGHT_MASK;
-	if (index > radix_tree_maxindex(height))
-		return 0;
+	while (radix_tree_is_indirect_ptr(node)) {
+		int offset;
 
-	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
+		shift -= RADIX_TREE_MAP_SHIFT;
+		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 
-	for ( ; ; ) {
-		int offset;
+		parent = indirect_to_ptr(node);
+		offset = radix_tree_descend(parent, &node, offset);
 
-		if (node == NULL)
+		if (!node)
 			return 0;
-		node = indirect_to_ptr(node);
-
-		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
-		if (!tag_get(node, tag, offset))
+		if (!tag_get(parent, tag, offset))
 			return 0;
-		if (height == 1)
-			return 1;
-		node = rcu_dereference_raw(node->slots[offset]);
-		if (!radix_tree_is_indirect_ptr(node))
-			return 1;
-		shift -= RADIX_TREE_MAP_SHIFT;
-		height--;
+		if (node == RADIX_TREE_RETRY)
+			break;
 	}
+
+	return 1;
 }
 EXPORT_SYMBOL(radix_tree_tag_get);